Since their introduction a few years ago, self-adhesive postage stamps have enjoyed tremendous popularity. In a typical construction, a sheetlet of self-adhesive postage stamps includes a laminate of an array of postage stamps made of a die-cut face stock, printed on one side with postage indicia, adhered to a release liner by a pressure-sensitive adhesive (PSA). U.S. Pat. No. 5,296,279 (Birnbaum et al.), assigned to Avery Dennison Corporation, is representative. ATM-dispensable, self-adhesive postage stamps are also known, and are disclosed in U.S. Pat. No. 5,503,436 (Alpaugh et al.), also assigned to Avery Dennison Corporation. Both patents are incorporated herein by reference.
The United States Postal Service (USPS) sets standards for United States-issued postage stamps. Government specification USPS-P-1238C (Jan. 24, 1996), which is incorporated by reference herein, identifies and describes certain "required," "target," and to-be-"monitored" properties of face stocks, adhesive layers (PSAs) and release liner backings (as well as linerless release coatings) to be used in self-adhesive postage stamps. An important property of self-adhesive postage stamps is the ability to form a permanent adhesive bond, after a short dwell time, to a variety of substrates, including woven paper, regular kraft, corrugated board, polyethylene based envelope stock (e.g., Tyvek.RTM., sold by DuPont de Nemours, E.I., Co. of Wilmington Del.), and other materials commonly used in envelopes and parcels. To deter theft and re-use of stamps, it is desirable that the adhesive leave a telltale fiber tear mark on the paper envelope or package if attempts are made to remove the stamp.
Although progress has been made in the area of self-adhesive postage stamps, a need for improved adhesives and theft-deterring stamp constructions continues to exist. In addition, the USPS has expressed a desire for "environmentally benign" self-adhesive postage stamps that can be recycled during ordinary paper recycling processes, or at least easily removed from envelope substrates prior to repulping and other recycling processes.
It is well-known that many PSAs contribute to the formation of what are commonly referred to in the trade as "stickies." Stickies tend to deposit on the felts, wires, drier cans, and other paper machine parts, and disrupt the smooth operation of paper machines. They also degrade the functional and cosmetic properties of paper products made with recycled paper filer. A need exists for self-adhesive stamps that either do not contribute to stickies formation or can be easily removed, preferably with water, before waste envelopes and parcels are repulped and recycled.